The present invention relates generally to skylights, and more particularly to tubular skylights, which use an enclosed hollow passageway, or light tunnel, to convey the sunlight from the energy-collecting aperture (or skylight) on the roof, to the energy-delivering aperture (or luminaire) inside the building. The present invention further relates to a passive skylight, with no moving parts, as opposed to an active skylight, with sun-tracking reflectors or lenses.
Mass-produced passive tubular skylights are becoming increasingly popular due to their relatively low cost, compared to conventional skylights, which use expensive frame-and-plasterboard construction of the light passageway from the energy-collecting aperture to the interior of the room. However, neither the prior art tubular skylight nor the conventional skylight is very effective in providing good illumination, throughout the entire day, in the room area just beneath the skylight, because of the highly variable angles of incidence of the rays of solar radiation intercepting the energy-collecting aperture.
Prior art passive tubular skylights and conventional skylights with tubular features have been the subjects of patents for more than 80 years. In U.S. Pat. No. 1,254,520, MacDuff describes a passive tubular skylight with numerous prisms and two mirrors located inside the energy-collecting dome on the roof of the building. The apparent purpose of the prisms and mirrors was to collect solar radiation, coming from a variety of directions with various incidence angles at the light-collecting dome, and to collimate and redirect such radiation downward through a light tube, into the interior of the building. As will be shown below, MacDuff""s arrangement is not feasible when the second law of thermodynamics is fully considered.
In U.S. Pat. No. 3,511,559, Foster describes a passive tubular skylight similar to MacDuff""s device, both using a large roof-mounted dome to collect sunlight from all directions. However, inside the dome, Foster uses a refractive collimator instead of the prisms and mirrors of MacDuff""s design. As will be shown below, Foster""s refractive collimator is not feasible when the second law of thermodynamics is fully considered.
In U.S. Pat. No. 4,114,186, Dominguez describes a passive tubular skylight with a movable reflective lid at the energy receiving end of the skylight. The lid could be opened to augment energy collection during the day, and closed to prevent energy leakage during the night. No means of collimating the sunlight are described by Dominguez.
In U.S. Pat. No. 4,306,769, Martinet describes a passive tubular skylight similar to MacDuff""s device, both using mirrors inside the energy-collecting dome to intercept and redirect incident sunlight. Martinet""s light tube is tapered from a relatively large opening near the energy collecting dome to a relatively small and constant opening for the light passageway from exterior roof to interior ceiling. As will be shown below, such a reduction in light tube width or diameter from the energy-capturing aperture to the energy-delivering luminaire is counterproductive in terms of light collimation.
In U.S. Pat. No. 4,733,505, Van Dame describes a passive tubular skylight constructed from a cloth-like fabric coated with reflective material. No means of collimating the sunlight are described by Van Dame.
In U.S. Pat. No. 4,809,468, Bareiss describes a conventional skylight light well constructed from a rolled-up flexible sheeting material to form a tubular light well structure. No mention of reflection, collimation, or other optical function of the skylight is made by Bareiss.
In U.S. Pat. No. 5,099,622, Sutton describes a passive tubular skylight, similar to those described earlier by MacDuff and Martinet, all of which use a reflector inside the energy-collecting dome on the roof of the building. As with the earlier designs, the purpose of Sutton""s reflector is to intercept and redirect sunlight downwardly into the light tube. No mention of collimation is made by Sutton.
In U.S. Pat. No. 5,546,712, Bixby describes a passive tubular skylight with improved mounting lips on the tubular sections comprising the light passageway. No mention of collimation is made by Bixby.
In U.S. Pat. No. 5,655,339, DeBlock describes a passive tubular skylight similar to the earlier designs of MacDuff, Martinet, and Sutton, all of which use reflective surfaces inside the energy-collecting dome to intercept and redirect sunlight downwardly into the light passageway. DeBlock""s reflector is a prismatic device molded into the dome itself No mention of collimation is made by DeBlock.
While not directly applicable to the present invention, other inventors have described active sun-tracking mirrors or lenses to provide downward collimation of sunlight into skylights. For example, in U.S. Pat. No. 4,883,340, Dominguez describes an active sun-tracking set of slatted mirrors for directing sunlight into a skylight. Similarly, in U.S. Pat. No. 5,729,387, Takahashi et al. describe an active, sun-tracking set of prismatic lenses for directing sunlight into a skylight.
As summarized above, the art contains many approaches to passive tubular skylights and to conventional skylights with tubular features. However, none of the prior devices disclosed in the art include practical means for collimating the collected sunlight so that it may be delivered to the desired location within the room below throughout the entire day. Indeed, prior passive tubular skylights which recognize the need for such collimation, including those illustrated in patents issued to MacDuff, Foster, and Martinet, present configurations which cannot provide such collimation because of a fundamental physical principle, as set forth in the second law of thermodynamics. The other prior skylights do not recognize or address the need for such collimation.
The present invention relates to an improved passive tubular skylight configured to collimate and deliver the collected sunlight to the desired area of the room directly beneath the luminaire, throughout the entire day. In a general embodiment, the skylight of the present invention comprises an energy-collecting aperture, an energy-delivering aperture and a specularly reflective light passageway disposed between said energy-collecting and energy-delivering apertures. The light passageway includes a specularly reflective collimating section which has a first cross-sectional area A1 for accepting light from the energy-collecting aperture and a second cross sectional area A2 for delivering light to said energy-delivering aperture. In a preferred embodiment, A2 is at least fifteen percent larger than A1.
The present invention is a purely passive collimating tubular skylight, which avoids the complexity, cost, and reliability disadvantages of all of the active skylight approaches.
Accordingly, several objects and advantages of the invention are to provide improved passive tubular skylights, said improved skylights providing better overall optical performance than prior art skylights. Other objects and advantages of the invention include improved passive tubular skylights, said improved skylights providing better collimation of the collected sunlight.
Other objects and advantages of the invention include improved passive tubular skylights, said improved skylights providing better all-day illumination in the desired working area beneath the skylight. Still further objects and advantages of the invention include improved passive tubular skylights, said improved skylights providing better throughput optical efficiency. Still further objects and advantages of the invention include improved passive tubular skylights, said improved skylights providing better light distribution within the interior space of the building.
Still further objects and advantages will become apparent from a consideration of the ensuing description and accompanying drawings.